1. Field of the Invention
This invention pertains to an electric power supply system and more particularly to an electric power supply system that includes a power grid source and an electrical power generation source (generator) with a switching mechanism that 1) electrically isolates the grid from the power generation device, 2) starts a power using device (load ) from the grid and 3) uses the power generation device for operating the load after initial startup from the grid. By using grid startup, the generator can be "undersized" to meet running rather than startup load capacity. In addition, the generator can also be used as a backup electrical supply when the power grid is down. In such instances, the "undersized" generator is fully utilized by using intelligent load control to schedule startup and operation of critical circuits.
2. Background of the Invention
Many changes are occurring in the electric power industry due to utility deregulation and opening of competitive markets. One such change is the increased importance of pricing electricity according to its value to the customer and its actual cost of delivery. The cost of delivering electricity is a strong function of demand and varies substantially during the course of the day and season.
At present, most residential and light commercial electric customers are charged a flat rate for electricity that is the same throughout the year or which may vary from season to season. Advanced technology for metering and data transmission is fostering electric meters that allow for real-time pricing of electricity to all customers including residential customers. Real time pricing allows electricity providers to vary the cost of power to the consumer at different times during the day and season depending on the cost of generation, transmission, and distribution capacity and other market conditions that prevail at the time. The result is lower power cost during off-peak periods and higher cost during on-peak periods. The demand for electric air conditioning usually occurs during on-peak periods in most utility areas. Therefore, the cost of power for air conditioning is expected to be substantially greater in the future than at present even though the total cost of power in aggregate may be lower.
Another effect of electric industry deregulation is possible lower reliability of grid power. This effect, even if it does not occur, will, at a minimum, cause anxiety among customers. When combined with already existing anxiety over power outages due to natural disasters, this is expected to cause increasing demand for standby or emergency on-site power generating capability.
However, the present approach to on-site power genration leaves much to be desired. Presently homeowners and small businesses purchase and install standby generators to provide power only during periods when power from the electric grid is not available. These devices typically work through an automatic transfer switch which activates the generator upon loss of grid power and transfers selected "critical loads" from the grid bus to the power feed from the generator. Critical loads typically include food storage (refrigerator and freezer), furnace, sump pump, well pump (for those having water wells), and at least one lighting circuit which in a growing number of cases can amount to a home office.
The starting of electric motors (all but for the lighting load listed above) has a significant impact on generator sizing. A typical motor often requires a starting current three or more times the current required for steady run. Thus, a motor normally requiring 1 kW to run (such as a furnace blower or refrigerator compressor) may require a generator having 3 to 5 kW of available capacity for starting. This becomes problematic for generators used in standby service because the generator must be sized for the worst case load. Such a scenario for a typical household having a standby generator is present below in Table 1.
TABLE 1 Worst Case Critical Load for Standby Generator Sizing Device Starting Load Running Load Refrigerator 2200 700 Freezer 2200 700 Sump Pump 2100 1000 Well Pump 2100 1000 Lighting 1000 1000 Furnace 2350 875 TOTAL 11950 5275
As is readily apparent, on-site power generation tends to be expensive because of the large generator capacity needed under start-up conditions. Further this capacity is little used since outages tend to be infrequent and of limited duration.
As such, it is an object of the present invention to provide a system that reduces the cost of power for large power load devices.
It is an object of the present invention to provide a system that reduces the cost of power for air conditioning systems.
It is an object of the present invention to provide a system that provides standby power for critical needs during power outages.
It is an object of the present invention to provide a system that utilizes a fossil fuel engine to generate electrical power.
It is an object of the present invention to provide an electrical power generating system with a driving engine having a long life.
It is an object of the present invention to provide an electrical power generating system with a driving engine having high efficiency.
It is an object of the present invention to provide a relatively small electrical power generating system that avoids large start-up electrical energy draws on the system.
It is an object of the present invention to provide an electrical power generator of a reduced size to match only the running load of electrically operated appliances.
It is an object of the present invention to provide a switch for providing start-up power to an electrically operated device from the power grid and then running the device from a power generator.
It is an object of the present invention to provide a power generating device that affords power shaving (energy cost reduction) for an electrically operated device during peak power grid periods and backup power for one or more critical power needs during grid power outage.
It is an object of the present invention to provide a power generating device and switch that allows startup of an electrical device from a power grid followed by running operation after startup of the electrical device from the power generating device and the use of the power generating device as a source of backup power for one or more critical power needs during grid power outage.
It is an object of the present invention to use optimally, an undersized power generating device by selectively and intelligently scheduling a critical load inventory.